I am selling a bike to someone I don't know from Craigslist. I expect that the prospective purchaser will want to test ride the bike before making the purchase.
How can I prevent them from riding away with my bike during a test ride?
The simplest answers are ask for their ID, or for their car keys if they arrive by car. There are plenty of other options on various forums like
Go to a Skatepark, usually there you have access limited by one or two doors, they are usually free, it's a good place to test a whip, you have mostly good visibility and riders, and depending on your location it may even have guards.
In this kind of eviroments if you shout "thief" or "help" skaters and bikers will help in my experience, they like their skate parks to have a good rep and they tend to push away sketchy people, altough YMMV.
I've just sold a bike. The buyer left their bike locked to the fence next to myself place. I offered to test ride as long and far as they consider necessary. If they wouldn't have turned up I should have waited there until they recovered their bike.
If that would have taken unusually long I should have put my own lock at their bike and inform them via email or text message.
A lot of people are saying to take the ID, but isn't checking the ID sufficient? Besides, there are other things, like a bank statement, which confirm the name and on top of that their address.
I guess if you live close to the buyer you could ask to meet them at theirs. You see them leaving their house, how exactly are they going to hide from you?
Another idea is to pick a good spot. A tennis court for example would be naturally closed off, stand next to the only gate and voila, they'd have to use force to get away with the bike.
Also, sometimes just the good-old first impression is sufficient. You can base the decision of whether you will let them try it out on that.